| 1. |
- Sierpowska, Joanna, et al.
(author)
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Effect of human trabecular bone composition on its electrical properties.
- 2007
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In: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 29:8, s. 845-852
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Journal article (peer-reviewed)abstract
- Mechanical properties of bone are determined not only by bone mineral density (BMD), but also by tissue trabecular structure and organic composition. Impedance spectroscopy has shown potential to diagnose trabecular bone BMD and strength, however, the relationships between organic composition and electrical and dielectric properties have not been systematically investigated. To investigate these issues organic composition of 26 human trabecular bone samples harvested from the distal femur and proximal tibia was determined and compared with relative permittivity, loss factor, conductivity, phase angle, specific impedance and dissipation factor measured at wide range (50 Hz to 5 MHz) of frequencies. A strong linear correlation was found between the relative permittivity at 1.2 MHz and trabecular bone fat content (r = -0.85, p<0.01, n=26). On the other hand, relative permittivity measured at 200 Hz served as a good predictor of water content (r = 0.83). Phase angle, specific impedance and especially conductivity were strongly related to the trabecular bone dry density and water content (|r| > or = 0.69). Variation in bone tissue collagen content was strongly related to the relative permittivity measured at 1.2 MHz (r = 0.64), but only moderately to other parameters. Glycosaminoglycan content showed no significant relations with any investigated electrical parameters. The present study indicates that if the trabecular bone composition is known, the relationships presented in this study could facilitate calculation of current field distribution, e.g. during electrical stimulation of osteogenesis. On the other hand, our results suggest that permittivity measured at low (<1 kHz) or high (>100 kHz) frequencies could be used, e.g. during implant surgery, for prediction of trabecular bone water or fat contents, respectively.
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| 2. |
- Jönsson, Bo-Anders
(author)
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A case study of successful e-learning: A web-based distance course in medical physics held for school teachers of the upper secondary level
- 2005
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In: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 27:7, s. 571-581
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Journal article (peer-reviewed)abstract
- Learning activities and course design in the new context of e-learning, such as in web-based courses involves a change both for teachers and students. The paper discusses factors important for e-learning to be successful. The development of an online course in medical physics and technology for high school teachers of physics, details of the course, and experience gained in connection with it are described. The course syllabus includes basics of radiation physics, imaging techniques using ionizing or non-ionizing radiation, and external and internal radiation therapy. The course has a highly didactic approach. The final task is for participants to design a course of their own centered on some topic of medical physics on the basis of the knowledge they have acquired. The aim of the course is I to help the teachers integrate medical physics into their own teaching. This is seen as enhancing the interest of high school students in later studying physics, medical physics or some other branch of science at the university level, and as increasing the knowledge that they and people generally have of science. It is suggested that the basic approach taken can also have applicability to the training of medical, nursing or engineering students, and be used for continuing professional development in various areas. (c) 2005 IPEM. Published by Elsevier Ltd. All rights reserved.
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| 3. |
- Sandberg, Frida, et al.
(author)
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Predicting spontaneous termination of atrial fibrillation using the surface ECG
- 2006
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In: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 28:8, s. 802-808
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Journal article (peer-reviewed)abstract
- By recognizing and characterizing conditions under which atrial fibrillation (AF) is likely to terminate spontaneously or be sustained, improved treatment of sustained AF may result and unnecessary treatment of self-terminating AF avoided. Time-frequency measures that characterize AF, such as fibrillatory frequency, amplitude, and waveform shape (exponential decay), are extracted from the residual ECG following QRST cancellation. Three complexity measures are also studied, characterizing the degree of organization of atrial activity. All measures are analysed using a training set, consisting of 20 recordings of AF with known termination properties, and a test set of 30 recordings. Spontaneous termination was best predicted by a low and stable fibrillatory frequency and a low exponential decay. Using these predictors, 90% of the test set was correctly classified into terminating and sustained AF. Neither fibrillation amplitude nor the complexity measures differed significantly between the two sets. (c) 2005 IPEM. Published by Elsevier Ltd. All rights reserved.
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| 4. |
- Sandsten, Maria, et al.
(author)
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Estimation of HRV spectrogram using multiple window methods focussing on the high frequency power
- 2006
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In: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 28:8, s. 749-761
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Journal article (peer-reviewed)abstract
- In this paper, the results of different multiple window spectrum analysis methods are compared in the estimation of heart rate variability (HRV) power spectra, in the high frequency band (HF), around 0.25 Hz, related to respiratory sinus arrhythmia (RSA). The evaluation is performed by simulating different spectrum shapes and peak frequency locations and calculating the mean squared error of a frequency range close around the strongest spectral peak. The results show that it is preferable to use the Peak Matched Multiple Windows in most situations, but the Welch method and the Sinusoid Multiple Windows can be as reliable in certain aspects.
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| 5. |
- Sebelius, Fredrik, et al.
(author)
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Classification of motor commands using a modified self-organising feature map.
- 2005
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In: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 27:5, s. 403-413
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Journal article (peer-reviewed)abstract
- In this paper, a control system for an advanced prosthesis is proposed and has been investigated in two different biological systems: (1) the spinal withdrawal reflex system of a rat and (2) voluntary movements in two human males: one normal subject and one subject with a traumatic hand amputation. The small-animal system was used as a model system to test different processing methods for the prosthetic control system. The best methods were then validated in the human set-up. The recorded EMGs were classified using different ANN algorithms, and it was found that a modified self-organising feature map (SOFM) composed of a combination of a Kohonen network and the conscience mechanism algorithm (KNC) was superior in performance to the reference networks (e.g. multi-layer perceptrons) as regards training time, low memory consumption, and simplicity in finding optimal training parameters and architecture. The KNC network classified both experimental set-ups with high accuracy, including five movements for the animal set-up and seven for the human set-up.
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| 6. |
- Stasiunas, Antanas, et al.
(author)
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Compression, adaptation and efferent control in a revised outer hair cell functional model
- 2005
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In: Medical Engineering and Physics. - Amsterdam : Elsevier. - 1350-4533 .- 1873-4030. ; 27:9, s. 780-789
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Journal article (peer-reviewed)abstract
- In the cochlea of the inner ear, outer hair cells (OHC) together with the local passive structures of the tectorial and basilar membranes comprise non-linear resonance circuits with the local and central (afferent–efferent) feedback. The characteristics of these circuits and their control possibilities depend on the mechanomotility of the OHC. The main element of our functional model of the OHC is the mechanomotility circuit with the general transfer characteristic y = k tanh(x − a). The parameter k of this characteristic reflects the axial stiffness of the OHC, and the parameter a working position of the hair bundle. The efferent synaptic signals act on the parameter k directly and on the parameter a indirectly through changes in the membrane potential. The dependences of the sensitivity and selectivity on changes in the parameters a and k are obtained by the computer simulation. Functioning of the model at low-level input signals is linear. Due to the non-linearity of the transfer characteristic of the mechanomotility circuit the high-level signals are compressed. For the adaptation and efferent control, however, the transfer characteristic with respect to the initial operating point should be asymmetrical (a > 0). The asymmetry relies on the deflection of the hair bundle from the axis of the OHC.
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| 7. |
- Stasiunas, Antanas, et al.
(author)
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Physiologically inspired signal preprocessing for auditory prostheses : Insights from the electro-motility of the OHC
- 2008
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In: Medical Engineering and Physics. - Oxford, England : Elsevier. - 1350-4533 .- 1873-4030. ; 30:2, s. 171-181
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Journal article (peer-reviewed)abstract
- We designed a non-linear functional model of the outer hair cell (OHC) functioning in the filtering system of the cochlea and then isolated from it two second-order structures, one employing the mechanism of the somatic motility and the other the hair bundle motion of the OHC. The investigation of these circuits showed that the main mechanism increasing the sensitivity and frequency selectivity of the filtering system is the somatic motility. The mechanism of the active hair bundle motion appeared less suitable for realization of the band-pass filtering structures due to the dependence of the sensitivity, natural frequency and selectivity on the signal intensity. We combined three second-order filtering structures employing the mechanism of the somatic motility and the lateral inhibition to form a parallel-type filtering channel of the sixth order with the frequency characteristics of the Butterworth-type and Gaussian-type. The investigation of these channels showed that the Gaussian-type channel has the advantage over the Butterworth-type channel. It is more suitable for realization of a filter bank with common lateral circuits and has less distorted frequency characteristic in the nonlinear mode.
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| 8. |
- Tabakov, S, et al.
(author)
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Development of educational image databases and e-books for medical physics training
- 2005
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In: Medical Engineering & Physics. - : Elsevier BV. - 1873-4030 .- 1350-4533. ; 27:7, s. 591-598
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Journal article (peer-reviewed)abstract
- Medical physics education and training requires the use of extensive imaging material and specific explanations. These requirements provide an excellent background for application of e-Learning. The EU projects Consortia EMERALD and EMIT developed five volumes of such materials, now used in 65 countries. EMERALD developed e-Learning materials in three areas of medical physics (X-ray diagnostic radiology, nuclear medicine and radiotherapy). EMIT developed e-Learning materials in two further areas: ultrasound and magnetic resonance imaging. This paper describes the development of these e-Learning materials (consisting of e-books and educational image databases). The e-books include tasks helping studying of various equipment and methods. The text of these PDF e-books is hyperlinked with respective images. The e-books are used through the readers' own Internet browser. Each Image Database (IDB) includes a browser, which displays hundreds of images of equipment, block diagrams and graphs, image quality examples, artefacts, etc. Both the e-books and IDB are engraved on five separate CD-ROMs. Demo of these materials can be taken from www.emerald2.net.
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